Process for the reduction of metal oxides by gases



Sept. 2, 1952 A. T. STUART PROCESS FOR THE REDUCTION OF METAL OXIDES BY GASES Filed March 8, 1950 2 SHEETS-SHEET l ATTORNEYS Sept. 2, 1952 A.'T STUART 2,609,288

PROCESS FOR THE REDUCTION OF METAL OXIDES BY GASES Filed March 8. 1950 2 SHEETS-SHEET 2 IN VENTOR ATTORNEYS Patented Sept. 2', 1 952 PRC-S'S-FORTH ..0X'IIES BY GSES K. ,emanan-Thomas stuart, .aeceasea'1ate @farm roto, Ont'ario, Canada., liyIs'obeVEL Stuart", executrix, Toronto; 'Ontari 'Canada Amplia-ation Marchas, 195o. serianNn. mm2.

In Canada; Marchf8,.19.49=

.12 .This inventionv pertains. to. the. .reduction of metallic `.oxides to. .metallby gaseousnneans..

Steel companies .and expertsin manylcoun't'ries,y at. .enormous` expense, have attempted Lto. com.-

mercialize. a number. oi processesor. themannf iactureof spongeironbygaseous reduction. 'Ehi-.- perience has taught that only two gases, hydro.- gen and carbon .monoxide .onmixtures thereof, are.. suitable .as..reducing..agents, and `that otherfuls. suchas .coal, coke,. oil, natural. gas vand'liydrocarbon gases shoul'drst .he'reformedV into hydrogen and, oarbonmonoxide gases.. Whatilittle success has `heen met with heretoforajhas heen.

attained' with an'extravagant use. of'fuels and'- energy.

"Most gaseous reduction processes involvel the continuous `movement of solids down a;- -shatorVY through' a kiln in" a direction* countercurrent to a: "flow of;preheated vreducingl gases: 'Underthe most favourablev circumstances, Aas governed by" the`l equilibrium; only' about "1/4' tofrtlieV ygas-can `15e/utilized;inf-a snglepass; itaisithe'refore neces--V saryto Vcoolush'e` exiting `gasesf'and =tofremove the productsl (H2O and/or CO2) 'beforefthe'- unused portionsA canhbe recovered-fand-reheated tov 1190'0' F2 for recirculation. -Gonsequentlylarge -quan`titiesof"-heat are=lostin radiation; in-the gases leaving the reduction zone-and'1in ltheflsieatedl products nfl reduction'. Although some-lofi this heatY is recuperated'in' sometproce'ssesl; 'llosses are stillhigh; A

Processesf in:usenrzunderdevelopment depend upon the" production: ofi :ai mixture 1 comprisingC ai large portion'.ofioarbon.monoxidet with aismaller portion. of Lhydmgen, :for: the rreasonxthat much'` less heatf :cil '.reactionzneed be. .supplied 'than :V if:V hydrogenwereausednalone: Li-. ez.r.approximately' 188,0005113. t; :urs vversus:8].1.;0il05 .B;. ta '.u-Js .per. 2.0001bs2 of iron madel. On the ether-hand;

the..standardr methodsfoftmakingrwater:gaszthef.

gen. alone, or hydrogen mixed :with a ,1minimum.

quantityfor" carbon monoxide. -This `is amatter. of. great. concern inl areas.- devoid .offresources-in.

ly. usedinknowngprocesses. .'Insuchfaeas;

filers. are-.too expensive.. o. use. for the tureothe reducing gases which .are .ectrava ere. frequently .are .resourcesfin water .powen .by-which; pure 'hydrogen ...and'ioxygenfcan. .befeconomicllyl generatedlby. theelectrolysis. of water. .Thaelec trolyticjhydrogen,-without.any uellca'n be`.j1s`ed"' for..- the production. osponge4 iron. .v's'fliiclnearlhe. Ine'ltejol in electric .urnaces the. prduoti'oneof'. steelingots Amongihe many. industrial x'siesLfcutl theLby-product.oxygen,..referencelis .made o-the facttha't .oxygen is. being. used? Witha.minimum.` quantity. ofi' .coallor .eoliey for themanufactuie .o@ water .gas or evenlof V.further .quantitieso'f '.hyidlgmL gen.. Y A

It'is-.ohvious..that there .is great.need..inrfmanw regions. 'for. a process .andlapparatus.-canahle lofi' utilizing.. Water vpower., with. or'. without. a.'.mini. mum. Vquantity. .of .fuel .for the... manuff'actiire;n sponge iron in small or in large tonnages..dSo.:y known. process4 in. use. or. under .develpmntels'e- Wherehas..heen .designedloris capahleof.'.i'neleting,A these Vsneciications.. for. .the manufacture." sponge-iron., .As an..example,..reference. e.A made .to A1'.he}huge .deposits.ofliighlgradehenatita ore. in QuebecfLabrador. .border.=area -`in-.Canada. Where Water. rpower is -plentiful l andvyherefthrei are..no.resources..in. fuelof anyv Although. .thaq'uantity .of .heat ,requiredlhyvthet chemicalreactions much.'v greater, .it has-.heen established .bothon theoretical andiexperilnental evidencethat .purehydrogeniis moresdesirahleiin: other.. ,grounds Vthan .mixturefofff .hytfogenly with .carbon..monoxide; ..fo1:.instance,.itislmovvin` that pure. hydrogenwillereduceore .efeetivelyt att muclillwer temperatures than willlany,;miiture withcarhon .monoxide .The present'. .invention relates. to a .process.andlapliaratus drogen, or any mixtnreofhyldrogen WithQca'ibonl. monoxide. .is utilized for 'thereduction 'of '.oresLi' quantiti"eslittle'` above 'tneya'mountscheoreticalm needed'and"wherein heatlossesarelikewise littleij moreiyth'an 'the' theoretical.. Accordingly. "e present'. invention makes use" of` a. closed 'circiut from -which .the ,gaseous nproducts' for'eduction;

areeontinuousm removeolandthe reducing'. gases-.1

' non.v Likewisethe.presentiimemmmmakesi whicniieaye theirediitiong..

times the quantity of fresh preheated gas through the reduction zone than would at first seem to be essential. Therefore, in order to localize and to expedite reduction within a short zone, it "was found that it is preferable for the solids to rest periodically in the reduction zone While proportionally large quantities of preheated and fresh gases pass through the same zone, though it is to be understood that the invention is not limited to the solids resting in any zone. It was also found that the large quantity of heat transported from the reduction zone by the gases is much more than can be absorbed by ore descending a vertical shaft, and that al continuous vertical shaft apparatus of the usual type cannot be efficient.

Likewise, it was also found that a batch process is inefficient. If the solids remain at rest inan iri'sulated` container throughoutk a reduction process, it is necessary to pass an enormous quantity of hot gases through the solids in order to preheat, reduce and finally cool the product as well as the container itself each time. For the reason that a large batch would take many hours to complete a cycle and for the reason that only a small portion of the lheat emitted by the gases can be recovered in preheating a second batch, it follows that heat losses are enormous.

A In order to explain the invention simply, it will be illustrated as if the solids rested in each zone for vsuflcient time to complete any desired treatment, although it is to be understood that the invention is not limited to the solids resting in any of the zones. It may be pointed out that, if thesolids descend the shaft continuously, they do so'at a very slow rate and that the solids can be treated during their descent by gases as described herein.

One object of the invention is to use a shafttype apparatus and to use two separate and independent gas circuits, one chiefly for reduction and the other chieiiy for the transport of heat. The invention uses a relatively small reduction zone in which the preheated solids remain for a certain period of time. Freshly prepared and preheated gas is then passed through the reduction zone only and immediately withdrawn and passed to an apparatus capable of storing high temperature heat efficiently for a short time. The invention uses .two apparatuses capable Vof storing heat and consequently the flow of heated gas may be repeatedly reversed whereby the ore inthe reduction zone may be reduced from the top down and from the bottom up. When reduction is completed, this gas circuit is stopped and the solids are dropped Within the shaft by removal of solids at the bottom.

By this means, the hot reduced metal is dropped from the reduction zone and is replaced by a preheated charge from above. More ore is then added to the top of the shaft and the second circuit'of gas is introduced. For this, cooling gas is fed vertically up from the bottom to the top of the shaft and out to a gas holder. By this pro`` cedure, the heat content of the hot metal at the bottom of the shaft is washed upwards toward the top where the cold ore has been admitted.

Hot "gases are also passed into and through the.

reduction zone and thence up the shaft in order to'raise the temperature in the reduction zone to the" desired degree and in order to preheat some of the ore in the shaft above the reduction zone. Preheated solids now occupy the reduction zone and are ready for reduction by preheated gas. l

"Fresh reducing gasv is preheated by passage 4 through the heat storage unit and then is superheated to 1900 F. and fed directly into the reduction zone of the shaft. The hot gases are Withdrawn immediately after passing through the reduction zone and then go t0 a second heat storage unit.

The gases which are cooled by passage through the heat storage units contain the unconsumed portions of reducing gas plus the steam and any carbon dioxide formed in the reduction zone. These products are removed by usual methods and surplus reducing gases go to a gas holder for recirculation. Make-up is added to the system and reducing gases are pumped back to the plant.

From the description, it Will be seen that closed type gas circulators are used and that losses of reducing gases are negligible. Likewise, it will be seen that closed type circulators of sensible heat are used; the heat contained in the hot sponge iron is washed upwards to preheat the fresh charges of ore; the heat contained in the hot gases leaving the reduction zone are stored and washed back to the reduction zone in the succeeding cycle.

1f desired, 'nitrogen may be added to the re-` ducing gases to assist in the transport of heat. for which purpose the nitrogen content may be varied to any desired extent.

Hydrogen or amixture of hydrogenrand carbon monoxide may be used as the reducing agent, consequently the gaseous products of the reduction may be either steam alone or a mixture of steam and carbon dioxide. These products may be separated from the spent gases by'usual commercial methods, and the unused portions of the reducing gases may be recovered for re-use. The

process will be illustrated as if hydrogen alone at 1900 F. were used as the reducing agent, and as if the only gaseous product were steam; however, it is t0 be understood that the invention is not to be so limited and that a mixture of reducing gases at any suitable temperature may be used and that gaseous products other than steam may be formed.

Two or more heat storage units are used, either of the regenerator or recuperator types. The fresh hydrogen coming from the gas holder through a compressor is passed into the bottom of oneof the heat storage units which has been heated in a previous cycle of operation. This' preheated hydrogen is then heated to 1900 F.

in passage through a super-heater before it en' ters the reduction zone of the tapered shaft. In4 the reduction zone of the shaft, possibly,25% of the hydrogen (as governed by the equilibriumpipes back'to the gas holder.

' reduction zone of the shaft; from there vthe spent gas heats up the first mentioned heat storage unitl and the excess hydrogen goes to the gas holder'. Thus yallwaste heatA is recuperated for' use-inthe-nextsucceedihg'cycle'. The heat consumed bythe chemical reactions in the reduction zone of the shaft may-be` supplied in the superheater. This superheater' takes inthe hydrogen preheated bypassage through one of? the heat storage unitsand-superheatsit. by suitable regulating means, tol-9009.117; beforeit is fed to the reduction zone of the shaft- It will be-seenthat the superheater carrsupply all the heat necessary to make up thelosses by the chemical reactionsl and by radiation... The. superheater may vIoeproxzided with; internal electricalelements which heat. the incoming. hydro.- ganA `by' passage. over `the surfaces. of these; velec tric resistance elements- Onthe other' hand. the: superheater may comprise a:V pipe coil heated externally by electric elements. or. by flames vof burning fuel. In. a third methndr .thesuperheater may. ybe similarV in construction to' a heat .storage` unit, described just abone'. Thev brick worlec a superheater may beheatedprior tothe: passage ot hy-` drogen to a Vtemperature at ,or above; 190.0?. E; For this. purpose hot combustion. gases.. made by burning gas or oi-l. withza. considerable; excessz.oi

air (in. order to hold the maximum temperature ata certain ypuin-tiara, .used toy preheatnbrick. worlgzafter purging Awith; nitrogen ;and hydrogen,. the apparatus is ready for-usein superheatingg. hydrogen.

It is` obviousfrom the aboi/e: descriptionthat thenlosses of hydrogenandfthe sensiblefheatcon tained in the solids and. circulating. gaseswillbe s very small,A and that. the actual consumption of.

hydrogen and of heat will be little Amore than. the; theoretical.A The theoretical requirement of .reducinggas, for the degree ofgdeoxdation desired, is approximately 17,0 cubicfeet per tonofiron.; the; theoreticalheat requirement-is, 8114.900 B., t.:.u.. when pure hydrogen iS used, or 188,000 B. u .s when a; mixture comprising 2/3 carbon monoxide. and. 1/1. hydrogen is used. When-carbon mon Oxidey alone is used.. the process isexothermic.. Indescribing the. invention referencev will be. made tothe attached drawingsinnwhichz;

Figure 1 shows= a front1elevation of the. equip menty used; for the reduction ot. oxides.v by hy drogen.v 2isatopyiewoi the apparatus. Figure 3 shows a cross-section on the line. ci'. Figure; 1. All the. apparatus is suitably heat. insulated as indicated-in the drawings..v s l In the drawings, 3 is a pipe. leadinghydrogen. from. a gasometer and compressor tothe; bottom of. heat storage uni-t 4-. Ripe; 5 leads the: 'pre-l heatedhydrogen.. from 4; intossuperheater- Ii.. from. which; the hydrogen issues. at 19.00 E -byxpipee 1..Y Pipe; 'I then leads the. hot. hydrogen to.. bustle; pipeAv Il, throughtuyres; 9; and Vpcrtsi t0 intoA .the vertical', taperedishaft I I..V proximately 1900" E; then: travels' down vtli'rougl'l'r the; solids:- in shaft. IIv to. ports .tzl and. .out: .tof bustle pipe'. I3;` Theihotgases issuing frombustle pipee I -3travel'by pipe Il@ to `unheated superheater I5; their by pipe*A IB ntoi the. topofsheat storage unit I1.. `The intersticed brick in= I1'V becomes heatedf from the top down while cooled excess hydrogen plus steam or condensate lexitat Athe bottom by pi-pe'. I8. `Pipe IB-lleads-the excess ily-- drogen back Itothe g-as holders.

If desired, the 'ow of hydrogen maybe reversed at anytime. For' this purpose `the electricity 'isi tmned off: -in `superheater 6i. and' is turned on n;

superheater I5. Then after the solidsiiritheire'-.`-

duction .zonez of: the: shaft situated between ports t0 and.. I2 are completely reduced.. the. gas iicw4 through the heat storage units as described; is shut oii' by the closure of the cold Valves on pipes 3 and I8 at the bottoms of the. heat storage. units..

The solids in the tapered shaft II are lowered by operating the discharge mechanism: I9' which; moves back and forth across plate 20.-thereby pushing they solids into bin 2 I. When the solids; below ports I2 are discharged into bin. 2.I,..they will be replaced by a like Volume. of hot. sponge irondescending from the reduction Zone in'. the. shaft II between ports ID and, l2.. Similarly; ati other solids in the main shafty I.I= will likewise descend, so that some of theA space above. ports III V will become empty;

At the top ofthe main shaft- I I there is an ore holding compartment situated between the'ftwoore feed bells 22 and 23. Bell 22 is opened and ore is dropped into the top off the main shaft: IfI. Bell 22 is then closed and bell 2 3 is. opened whifle. fresh ore is dropped into the ore holding com-I partment. After bell 23 is closed, the atmosphere of the ore holding compartment is purged byleadi'ng hydrogen.' in at the top through pipe 2l and out at the bottom through pipe 25.

In the main shaft I I, the'si'tuation may beth-at cold oreV resides in the zone above ports IU; preheatedV ore resides in the reduction zone between ports I0 and I2; hot sponge iron resides in the zone below ports I2; bin 2I is empty.

rlhe second type of hydrogen circulation is now introduced in order totransfer the heat contained in the hot sponge iron vat the bottom ofshaft I I to the solids above ports I0. Cooling gas is therefore fed into bin 2| by pipe 26; and vertically upwards through the whole main shaft II- to the outlet pipe 2'I and thenceback tothe. gas holder. This circulation is continued `until the sponge iron in the bottom zone of the shaft'= is cooled. Hot gases-are then injected at ports I2 and, by suitable manipulation of the outlet Valves 3', I8 and 21, are caused to iiowfup the sha-ft I I to outlet 2'! and back to the gas-holder', in order to transport heat' and to raise the temperature in the reduction zone above ports I2- to theY desired degree and also to preheat and' dry some of the ore residing above the ports I0.'- To assist in the transport of' heat the per-f centage of nitrogen in thevcirculatinggases may ber increased. Nitrogen is not consumed and, since a closed circuit is used', Vnitrogen is notI lost andwill continue to, recirculate; therefore,v order to increase the percentage of nitrogen in the circulating gases, i-t is only-necessary to reduce or cut' on at any time the amount of' make-up hydrogen 'being' fed into the system.

TheV iirst typeA of hydrogen-circulation `previously described is now repeated, it being under# stood that' the direction of flow of the reducing gases Vthrough thereduction zone-is reversible: Fresh cool hydrogen enters the bottom of heat storageunit I'I bypipe I8, and thev hydrogen 'thus' preheated issues by pipe I6 into superheater 'I5 from which, by suitable regula-tion, it issues at l900 F. The l900 F'. hydrogen lthen flows by pipe I4 into the ports I2 of shaft I I, up through the solids in the reduction zone and out at ports IIJ. Pipe I leads the spent gas through uri*-l heated superheater E andl down pipe 5' into heat storage unit 4. From thebottom of unit l', pipe 3 conveys any condensate to a water trap 'and leads vexcess hydrogen back to the gas holder'.- Likew-ise, the reverse flow will bring vhot' hydrogen into the reduction zone atports ftU-'downthroug-h* thesolidsi the reductionzone andfout at ports.'

t2 '.to` heat storage unit IT which now lhas beL come cool.v This ends one lcomplete cycle of operations.

Although the process as described involves the use of hydrogen, it'is to be understood that other reducing gases may be used. When carbon dioxide is one of the gaseous products of reduction, it is removed from the cooled exit gases'by usual means and excess carbon monoxide, -as well as hydrogen, is recovered for re-use.

If desired, nitrogen may be added to the reducing gases to assist in the transport of heat. Also, the process and apparatus may be operated under considerable pressure.

:It is to be understood that the same features can be applied to a stationary batch process, where the solids remain at rest during the whole complete cycle of preheating, reducing and cooling and are not lowered from one zone to another zone, as in a shaft process. For instance, a heat insulated receptacle may be used which is filled with a single batch of ore and reduced, after which the sponge iron may be removed either hot or co1d.- Y

,i However, a preferred form of process and apparatus have been described which combines the best features of a continuous shaft process with those of a batch process. The solids and gases may both enter and leave the apparatus at normal temperatures, thus indicating very high thermal efficiency. On the other hand, it is evident that the sponge iron can be discharged in a hot condition where that may be desired.

Heretofore, no process or apparatus has been developed which is capable of commercially producing sponge iron by means of pure hydrogen. Experts of the steel industry have pointed to the peculiar properties of hydrogen, its unique heat conductivity, etc., and to the larger quantities of heat which must be supplied to a hydrogen process and the large installations in heat exchangers of the usual type which would be required. In short, it has been claimed that pure hydrogen cannot be commercially used in the manufacture of sponge iron as melting stock. Obviously, these authorities anticipated the use of fuel for the production of heat and the necessity of a partition separating combustion gases from reducing gases through which heat must be transferred.

-. These and other technical diiiculties were foreseen and fully considered in the development of the present invention. It was concluded that types of gas circulation, furnace-construction and heat exchangers new. to the gaseous reduction process must be introduced; at the same time provision must be made bywhich high temperature heat can be recovered and re-used. Also, it became evident that there should be no essential change in the composition of atmosphere used in the process. For instance, it is undesirabie to use an oxidizing atmosphere (i. e. hot combustion gases with excess air) in a process which primarily demands a reducing atmosphere, such as hydrogen.

Therefore the type of heat storage unit previously described is used in which, in addition to storing heat, heat exchange at virtually 100% efficiency is effected. This is done by avoiding any substantial change in the composition of the atmosphere of the heat storage units. This atmosphere may be reducing gas, with or without nitrogen flowing through the heat storage unit in one direction, or it may be reducing gas, with or without nitrogen, plus the gaseous products of reduction flowing in the opposite direction. The

exchange or heat is eiected bythe gases, without:

8. any substantial change in., composition; passing in either direction over the surface of the intersticed brick contained in the unit designated herein'as a heat storage unit. l

What is claimed is:

l. A process for the reduction of metal oxides Without fusion which comprises the steps of feeding oxide ore to a furnace havingr preheating, reduction and cooling zones one below the other, preheating and eiecting reduction of the ore by alternate cycles of gas circulation, the rst cycle comprising the circulation of a hot gas through the reduction and preheating Zones, the second cycle being a reducing cycle wherein hot reducing gas is circulated only through the reducing zone, withdrawing the gases from the furnace, repeating the reducing cycle until the ore is reduced, and removing the reduced metal from the furnace.

2. A process for the reduction of metal oxides without fusion which comprises the steps of feeding oxide ore to a furnace having preheating, reduction and cooling Zones one below the other, preheating and effecting reduction of the ore by alternate cycles of gas circulation, the first cycle comprising the circulation of a hot gas vthrough the reduction and preheating zones, the

second cycle being a reducing cycle wherein hot reducing gas is circulated only through the reducing zone, withdrawing the gases from the furnace, repeating the reducing cycle until the ore is reduced, removing the reduced metal from the furnace,V extracting heat and impurities from the withdrawn gases, and heating the gases to be used in new cycles of circulation by means of the extracted heat.

3. A process for the reduction of metal oxides Without fusion which comprises the steps offeeding oxide ore to a furnace having preheating, reduction and cooling zones one below the other, preheating and effecting reduction of the ore by alternate cycles of gas circulation, the first cycle comprising the circulation of a hot gas through the reduction and preheating zones, the second cycle being a reducing cycle wherein hot reducing gas is circulated only through the reducing zone, withdrawing the gases from the furnace, repeating the reducing cycle until the ore is reduced,A removing the reduced metal from the furnace, extracting heat and impurities from the withdrawn gases, heating the gases to be used in new cycles of circulation by means of the ex-l tracted heat, and superheating the reducing gas before it is recycled.

fl. A process for the reduction of metal oxides without fusion which comprises the steps of feeding oxide ore to a furnace having preheating, reduction and cooling zones one below the other,`

preheating and effecting reduction of the ore by..

alternate cycles of gas circulation, the rst cycle' comprising the circulation of a hot gas through the reduction and preheating zones, the second' cycle being a reducing cycle wherein hot reducing gas is circulated only through the reducing zone, withdrawing the gases from the furnace, repeating the reducing cycle until the ore is reduced, extracting heat and impurities from the withdrawn gases, heating the gases to be used in newv cycles of-circulation by means of the extracted heat, superheating the reducing gas before it is recycled, cooling the reduced metal by introducing a stream of cool gas at the bottom of the furnace, said gas after beingvheated bythe re-f duced metal carrying heat to the other zones of the furnace.

5. A process for the reduction of metal oxides without fusion which comprises the steps of feeding oxide ore into a furnace having preheating, reducing and cooling zones one Ibelow the other, preheating and effecting the reduction of the ore by a series of separate cycles of gas streams, each of said gas streams passing through distinct zones in the furnace, the rst cycle comprising the circulation of a hot gas through the reduction and preheating zones to effect preheating of the ore, the second cycle being a reducing cycle wherein a superheated reducing gas is .introduced immediately adjacent the reducing zone and continuously withdrawn from the furnace after passing through the reducing zone, extracting heat and impurities from all of the withdrawn gases, using the extracted heat to heat the gases used in additional cycles, superheating the reducing gas and recycling it through the reduction zone until reduction is completed, cooling the reduced metal and transmitting heat to the reduction and preheating zones by introducing a stream of cool gas at the bottom of the furnace and withdrawing at the top of the furnace, manipulating the respective cycles of gas circulation to maintain the furnace at operating temperature, and removing cool reduced metal fromthe furnace.

6. A process for the reduction of metal oxides without fusion which comprises the steps of feeding oxide ore into a furnace having preheating, reducing and cooling zones one below the other, preheating and effecting the reduction of the ore by a series of separate cycles of gas streams, each of said gas streams passing through distinct zones in the furnace, the first cycle comprising the circulation of a hot gas through the reduction and preheating zones to effect preheating of the ore, the second cycle being a reducing cycle wherein a superheated reducing gas is introduced immediately adjacent the reducing zone and continuously withdrawn from the furnace after passing through the reducing zone, extracting heat and impurities from all of the withdrawn gases and using the extracted heat to heat the gases used in additional cycles, superheating the reducing gas consisting of hydrogen and recycling it through the reduction zone until reduction is completed, cooling the reduced metal and transmitting heat to the reduction and preheating zones by introducing a stream of cool gas at the bottom of the furnace and withdrawing at the top of the furnace, manipulating the respective cycles of gas circulation to maintain the furnace at operating temperature. and removing cool reduced metal from the furnace.

7. A process for the reduction of metal oxides without fusion which comprises the steps of feeding oxide ore into a furnace having preheating, reducing and cooling zones one below the other, preheating and effecting the reduction of the ore by a series of separate cycles of gas streams, each of said gas streams passing through distinct zones in the furnace, the rst cycle comprising the circulation of a hot gas through the reduction and preheating zones to effect preheating of the ore, the second cycle being a reducing cycle wherein a superheated reducing gas is introduced immediately adjacent the reducing zone and continuously withdrawn from the furnace after passing through the reducing zone, extracting heat and impurities from all of the Withdrawn l0 gases and using the extracted heat to heat the gases used in additional cycles, superheating the reducing gas consisting of a mixture of hydrogen and anA inert gas and recycling it through :the reduction zone until reduction is completed.

cooling the reduced metal and transmitting heat to the reduction and preheating zones by introducing a stream of cool gas at the bottom of the furnace and withdrawing at the top of the furnace, manipulating the respective cycles of gas circulation to maintain the furnace at operating temperature, and removing cool reduced metal from the furnace.

8. A process for the reduction of metal'oxides without fusion which comprises the steps of feeding oxide ore into a furnace having preheating, reducing -and cooling zones vertically disposed to each other in the aforesaid relationship, preheating and effecting the reduction of the ore by a series of separate cycles of gas streams, each of said gas streams passing through distinct zones in the furnace, the first cycle comextracting heat and impurities from all of the n withdrawn gases and using the extracted heat to heat the gases used in additional cycles, superheating the reducing gas consisting of a mixture of hydrogen, carbon monoxide and an inert gas and recycling it through the reduction zone until reduction is completed, cooling the reduced metal and transmitting heat to the reduction and preheating zones by introducing a stream of cool gas at thefbottom of the furnace and withdrawing at the top of the furnace, manipulating the respective cycles of gas circulation to maintain the furnace'at operating temperature, and removing cool reduced metal from the furnace.

9. A process as claimed in claim 1, in which the circulation of reducing gas during the second cycle is reversed.

10. A process as claimed in claim 5, in which the circulation of reducing gas during the second cycle is reversed.

11. A process as claimed in claim 5, in which the reducing gas consists essentially of hydrogen and carbon monoxide.

ISOBEL ELIZABETH STUART, Eccecutri of the Estate of Alexander T. Stuart,

Deceased. Y

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,269,054 Clark et al. June 11, 1918 1,310,724 Westberg July 22, 1919 1,433,854 Sending-Larsen Oct. 31, 1922 1,824,960 Lawaczeck Sept. 29, 1931 2,142,100 Avery Jan. 3, 1939 2,166,207 Clark Jan. 13, 1939 2,231,760 Foerster Feb. 11, 1940 2,501,189 Pike Mar. 21, 1950 FOREIGN 'PATENTS Y Number Country Date 71,534 Sweden July 14, 1927 

1. A PROCESS FOR THE REDUCTION OF METAL OXIDES WITHOUT FUSION WHICH COMPRISES THE STEPS OF FEEDING OXIDE ORE TO A FURNACE HAVING PREHEATING, REDUCTION AND COOLING ZONES ONE BELOW THE OTHER, PREHEATING AND EFFECTING REDUCTION OF THE ORE BY ALTERNATE CYCLES OF GAS CIRCULATION, THE FIRST CYCLE COMPRISING THE CIRCULATION OF A HOT GAS THROUGH THE REDUCTION AND PREHEATING ZONES, 